3 Answers
3

They seems to put a correct redirection header (moved permanently, with the new URI), but maybe at the start, they don't do it correctly (redirection with JS). So, it cause a loss in the page rank of the original site, and just a share of the page rank of the original site to the new site…

Not true: "Use a 301 Redirect to permanently redirect all pages on your old site to your new site. This tells search engines and users that your site has permanently moved. We recommend that you move and redirect a section or directory first, and then test to make sure that your redirects are working correctly before moving all your content." --google.com/support/webmasters/bin/… It also tells search engines, 301'ed inlinks will pass PR to the new domain.
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Stephan MullerJan 26 '11 at 11:35

1

Also: "Matt Cutts: Typically, the 301 Redirect would pass PageRank. It can be a very useful tool to migrate between pages on a site, or even migrate between sites. Lots of people use it, and it seems to work relatively well, as its effects go into place pretty quickly. [...] At least for me, the 301 does work the way that I would expect it to. All the pages of interest make it over to the new site if you are doing a page by page migration, so it can be a powerful tool in your arsenal." -- stonetemple.com/articles/interview-matt-cutts-012510.shtml
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Stephan MullerJan 26 '11 at 11:39

You are confusing two issues. You need to read those quotes in context. Putting a 301 on a site will not directly transfer the PR or the exact search results across to the new site. Try it if you do not believe me.
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JamesRyanJan 26 '11 at 11:59

"Don't do a single redirect directing all traffic from your old site to your new home page. This will avoid 404 errors, but it's not a good user experience. It's more work, but a page-to-page redirect will help preserve your site's ranking in Google" so content matching must also be a factor and suggests that you prolly don't want to coincide a redesign with a change in domain
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JamesRyanJan 26 '11 at 12:30

I would like to chime in that you really don't need to worry about PR. Google itself says not to worry about PR. It's an older tool and was used as an indicator in the past, but it no longer carries the same weight that it used to.

To give you an example, I've been able to successfully outrank PR 6, 7, and 8 pages on a 2-word keyword phrase with 1.5M monthly hits (position 3 in Google) and the site is only PR5.

Elsewhere I've been able to rank PR 0, 1, and 2 sites for 3-word plus keyword phrases going against PR5+ sites and captured the top spot.

Long story short, focus on getting great links and building great content.